KR19990063633A - Difluoromethane Production Method - Google Patents

Abstract

The present invention provides a gas phase process for the preparation of difluoromethane, HFC-32. The method of the present invention provides a method for preparing HFC-32 by a method showing good production yield and selectivity.

Description

Difluoromethane Production Method

It is well known in the art that HFC-32 can be used as an alternative to environmentally disadvantaged chlorofluorocarbon refrigerants, blowing agents, and aerosol accelerators. Various methods for the gas phase preparation of HCF-32 are known.

For example, US Pat. No. 2,745,886 discloses a gas phase process for fluorination of various halohydrocarbons, including methylene chloride, HCC-30, which uses an oxygen activated hydrated chromium fluoride catalyst. Likewise, US Pat. No. 2,744,148 discloses a halohydrocarbon fluorination method in which an HF-activated alumina catalyst is used.

US Pat. No. 3,862,995 discloses gas phase preparation of HFC-32 by reaction of vinyl chloride with HF in the presence of a vanadium derivative catalyst supported on carbon. US Patent No. 4,147,733 discloses a gas phase reaction for the production of HFC-32 by HCC-30 and HF in the presence of a metal fluoride catalyst.

Indeed, such HFC-32 manufacturing methods suffer from a variety of problems, including low production yields and selectivity, as well as operational difficulties such as raw material degradation. The method of the present invention provides for the production of HFC-32 by a method that overcomes some of the disadvantages of the known methods.

The present invention relates to a gas phase process for the preparation of difluoromethane, HFC-32. More specifically, the present invention provides a method for producing HFC-32 which exhibits good production yield and selectivity.

The present invention provides a method for preparing HFC-32 with good yield and selectivity. The process of the present invention comprises the steps of contacting HCC-30 with HF in the presence of a fluorination catalyst to produce a product stream of difluoromethane, chlorofluoromethane ("HCFC-31"), hydrogen chloride, dichloromethane, and hydrogen fluoride; Separating HFC-32 from the product stream. In a preferred embodiment, the present invention comprises the following steps:

(A) preheating a composition comprising hydrogen fluoride (“HF”) and HCC-30 and, optionally, HCFC-31 to form an evaporated and superheated composition;

(B) reacting the preheated composition of step (A) in the presence of a fluorination catalyst under conditions suitable to form a product stream comprising HFC-32, HCFC-31 and HCC-30 and HF not reacted with hydrogen chloride;

(C) distillation of the high boiling point fraction comprising HF, HCC-30, and HCFC-31 and the low boiling point fraction containing HFC-32, HCl, HF and reaction by-products from distillation from the product stream of step (B) step;

(D) recovering substantially pure HFC-32 from the low boiling fraction of step (C).

In step (A), the composition comprising HF and HCC-30 is preheated in at least one evaporator. "Preheat" means evaporating and overheating the composition. The composition is heated to a temperature of about 125 ° C. to about 400 ° C., preferably 150 ° C. to about 300 ° C., more preferably about 175 ° C. to about 275 ° C., and most preferably 200 ° C. to about 250 ° C. The evaporator, as well as the other vessels used in this method, should be made of suitable corrosion resistant material.

Although fresh HF and HCC-30 can be used in step (A), the composition of step (A) preferably contains the regeneration material from step (C) as described below. If the process is carried out without continuous recycling, the molar ratio of HF to organics, in particular HF to HCC-30, is from about 1: 1 to 10: 1, preferably from about 1: 1 to about 4: 1. Optionally, fresh HCFC-31 can be added to the composition of step (A).

As an alternative, the continuous recycle stream of the high boiling fraction obtained in step (C) is recycled to step (A) in which excess HF for organics is used. In the process of the invention, the higher the molar ratio of HF to organics, the higher the yield and selectivity for HFC-32. Similarly, excess HF results in a decrease in the concentration of unreacted HCC-30 as well as the produced HCFC-31. In addition, especially when the reaction is carried out above 3 atmospheres, excess HF lowers the rate of deactivation of the catalyst to reduce degradation in the preheater and evaporator. In general, the ratio of HF to HCFC-31 measured at least about 25: 1 to at least about 300: 1, preferably at least about 50: 1 to at least about 200: 1, as measured after separation of HFC-32 from the product stream. More preferably between about 75: 1 and at least about 150: 1.

The preheated composition of step (A) is reacted in step (B) of the gas phase fluorination reaction to form a product stream mixture. The reaction can proceed in one or more isothermal or adiabatic reactors. If more than one reactor is used, the arrangement of the reactors is not critical, but sequential arrangement is preferred. Inter-reactor heating or cooling can be used to obtain the best reactor performance.

The reactor or reactors used in the process are filled with a fluorination catalyst and the organics and HF vapor are allowed to contact the catalyst under conditions suitable to form a reaction mixture. The reactor temperature is maintained at about 125 ° C to about 425 ° C, preferably at 150 ° C to about 300 ° C, more preferably at about 175 ° C to about 275 ° C, most preferably at 200 ° C to about 250 ° C. The reactor pressure is atmospheric pressure, atmospheric pressure, or superatmospheric. The reactor pressure is preferably maintained at about 0 psig to about 250 psig. The contact time, ie the time required for the reactants to pass through the catalyst bed, assuming a 100% pore catalyst bed, is usually about 1 to about 120 seconds, preferably about 2 to 60 seconds, more preferably about 4 to About 50 seconds, most preferably about 5 to about 30 seconds.

Any known gaseous fluorination catalyst can be used in the present invention. Examples of catalysts include, but are not limited to, chromium, copper, aluminum, cobalt, magnesium, manganese, zinc, nickel, and iron oxides, hydroxides, halides, oxyhalides and their inorganic salts, Cr ₂ O ₃ / Al ₂ O ₃ , Cr ₂ O ₃ / AlF ₃ , Cr ₂ O ₃ / carbon, CoCl ₂ / Cr ₂ O ₃ / Al ₂ O ₃ , NiCl ₂ / Cr ₂ O ₃ / Al ₂ O ₃ , CoCl ₂ / AlF ₃ And NiCl ₂ / AlF ₃ . In addition, supported metal catalysts such as nickel, cobalt, zinc, iron, and copper supported on chromium, magnesium, or aluminum can be used. Chromium oxide / aluminum oxide catalysts are described in US Pat. No. 5,155,082. Preferably, chromium oxide, which is a commercially available catalyst, is used. The chromium oxide may be crystalline or amorphous. Preferably, amorphous chromium oxide is used. The catalyst is used in an amount effective to induce the reaction.

The fluorination catalyst may be pretreated before introduction of the reaction feedstock, which is preferred. "Pretreatment" means chemically or physically changing the catalyst to make an active site on the catalyst where the reaction takes place. The catalyst is pretreated by calcination under a flow of inert gas such as nitrogen at a temperature of about 200 ° C. to about 450 ° C. for at least about 1 hour. The catalyst is then exposed to HF alone or a mixture with about 5 to 99% by weight of inert gas at a temperature of about 200 ° C. to about 450 ° C. for at least about 1 hour. Preferably, the catalyst then undergoes a third pretreatment step in contact with chlorine gas. Preferably, the chlorine is diluted with about 60 to about 75% HF and / or about 20 to about 30% inert gas. The chlorine passes through the catalyst at a total chlorine volume to total catalyst volume of 1: 3,000 v / v, preferably about 10: 1,000 v / v, more preferably about 50: 500 v / v. The exposure time is about 1 to 200 hours, preferably 5 to 70 hours, more preferably 10 to 30 hours. Chlorine exposure can be carried out at any temperature and pressure convenient for the fluorination reaction.

After completion of the pretreatment, the chlorine flow is stopped and HF and HCC-30 feed are introduced. Preferably, the fluorination reaction is performed for about 1 to 200 hours, preferably about 5 to 70 hours, and more preferably about 10 to 25 hours, and about 0.1 to about 10 mol% based on the organic content, Preferably a small amount of chlorine of about 2-8% should be added to the reactor to deactivate the catalyst to recover activity.

The product stream prepared in step (B) contains not only unreacted feedstocks such as HF and HCC-30, but also reaction products which are HFC-32, HCFC-31, and HCl. The product stream of step (B) is fed to the recycle column of step (C). The recycle column may be any standard distillation column known in the art. The high boiling point fraction, or bottom stream, from the recycle column consists of unreacted HF, HCC-30, and the reactant HCFC-31, which is an intermediate. Preferably, this mixture is recycled to step (A) after regeneration. Further in step (C), the low boiling point fraction of HFC-32, HCl, HF, or the top stream, and reaction byproducts are recovered.

Alternatively, step (C) may be performed in two parts. In the first part, the product stream of step (B) is cooled. By "quenching" is meant to reduce the temperature of the reaction mixture below its dew point. Cooling is done in a packed column containing any suitable corrosion resistant packing material and a suitable reflow liquid such as HF, HCC-30, and / or HCFC-31, after which the cooled product is fed to a recycle column.

In step (D), substantially pure HCFC-32 is recovered from the low boiling point fraction of step (C) by any method well known in the art. Step (D) is preferably carried out as a series of substeps comprising the step (E) of treating the gas mixture in an HCl distillation column or an aqueous HCl adsorption column under conditions suitable for removing HCl and traces of HF. The crude HFC-32 product of step (E) is then treated with a first caustic scrubber under conditions suitable to form the neutralized product by neutralizing the remaining acid groups in step (F). Typically, the caustic scrubber contains water, sodium hydroxide, or potassium hydroxide. The product of step (F) in a second caustic scrubber comprising sodium hydroxide, preferably with sulfurous acid such as sodium sulfite, under conditions suitable for removing residual chlorine to form a product which is actually chlorine free after step (F). Processing (G) is followed. In step (H), the product of step (G) is treated with a sulfuric acid scrubber and then treated with a solid desiccant, such as any suitable, commercially available molecular sieve that absorbs residual moisture from the gas stream to give the product that is virtually moisture free. Form. This is followed by step (I), in which the product of step (H) is run through a plurality of distillation columns under conditions sufficient to remove residual impurities to produce at least 99.97% by weight to produce substantially pure HFC-32. Any remaining HCFC-31 removed in) is recycled to step (A).

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1-2

A 1/2 inch Monel tube reactor was charged with about 110 ml of Cr ₂ O ₃ / Al ₂ O ₃ (40/60 wt.%) Coextruded catalyst. The catalyst was dried / calcined at about 400 ° C. for about 16 hours at 2-3 L / min using air. The temperature was then lowered to 200 ° C. and air was replaced with nitrogen at a rate of about 0.5-1.5 L / min. Anhydrous HF was pumped into the reactor until the exotherm passed through the reactor. The temperature was then increased by 25 ° C. every half hour and maintained at that temperature for 8 hours when the temperature reached about 350-400 ° C. The temperature was then lowered to the desired reaction temperature. HF and HCC-30 were fed to the reactor in a molar ratio of 4: 1 (HF: HCC-30). The mixture of HF and HCC-30 passed through two preheaters, the first of which was about 100-185 ° C and the second about 200-275 ° C. The pressure was 50 psig and the reactor temperature was 275 ° C. in Example 1 and 300 ° C. in Example 2. For Example 1, the contact time was 16 seconds, resulting in 82% conversion and 89.3% HFC-32 selectivity. Productivity was 10 lbs HFC-32 / hr / ft ³ . The productivity of HFC-32 in Example 2 was 13.6 lbs / hr / ft ³ and the selectivity of HFC-32 was about 85%. The results of this example are summarized in Table I.

Table I

Example 1 Example 2 catalyst Cr ₂ O ₃ / Al ₂ O ₃ (40/60 wt%) Cr ₂ O ₃ / Al ₂ O ₃ (40/60 wt%) pressure 50 psig 50 psig HF / HCC-30 4 4 Temperature ℃ 275 300 Contact time (seconds) 16 10 % Conversion ₂ CH ₂ Cl ₂ 82 77 Selectivity (%) HFC-32HCFC-31HCC-40 89.310.60.1 84.715.20.1 Productivity (lbs / hr / ft ³ ): HFC-32 10.3 13.6

Examples 3-6

In the tube reactors of Examples 1 and 2, about 100-110 ml of Cr ₂ O ₃ / Al ₂ O _{3 in a} weight ratio of 78/22 was packed. The catalyst was dried / calcined and HF treated using the same procedure as in Examples 1 & 2. The HF and HCC-30 mixture was passed through the same preheater as shown in Examples 1 & 2. Pressures, contact times, and results are shown in Table II.

Table II

Example 3 Example 4 Example 5 Example 6 catalyst Cr ₂ O ₃ / Al ₂ O ₃ (78/22 wt%) Cr ₂ O ₃ / Al ₂ O ₃ (78/22 wt%) Cr ₂ O ₃ / Al ₂ O ₃ (78/22 wt%) Cr ₂ O ₃ / Al ₂ O ₃ (78/22 wt%) Pressure (psig) 50 200 225 225 Molar ratio of HF / CH ₂ Cl ₂ 4 4 4 4 Temperature (℃) 275 275 275 275 Contact time (seconds) 11 36 40 26 Conversion Rate (% CH ₂ Cl ₂ ) 71 70 70 61 Selectivity: HFC-32HCFC-31HCC-40 82180.05 81190.05 81190.05 77230.05 Productivity (lbs / hr / ft ³ ): HFC-32 12 12 12 15

Example 7

4 L of chromium oxide catalyst was charged to a 4 inch diameter Monel 400 reactor. The catalyst was dried under 20 slpm nitrogen flow for 8 hours at 350 ° C. After reducing the catalyst bed temperature to 250 ° C., anhydrous HF was added to flowing nitrogen at a flow rate of 0.2 lbs / hr. The flow rate of the HF gradually increased to 1.0 lb / hr and the temperature was raised to 350 ° C. and maintained for 4 hours. The catalyst bed was then reduced to 250 ° C. and chlorine was introduced into the HF / N ₂ mixture at a rate of 500 sccm for 24 hours.

After this pretreatment, the chlorine and nitrogen streams were stopped and HCC-30 was mixed with HF and passed through a preheater at 185 ° C. The evaporated HCC-30 and HF mixture was fed to a pressure 45 psig reactor, and the effluent from the reactor was cooled using a heat exchanger and injected into a distillation column maintained at 50 psig. The low boiling distillation components, HCFC-31, HF, and HCC-31, were recycled again, mixed with fresh HF and HCC-30 feed streams, fed to the preheater, and injected into the reactor at a rate of 4.6 lbs / hr. The recycle stream contained HF: HCFC-31 in a molar ratio of 360: 1. The recycle material was mixed with additional HF and HCC-30 at flow rates of 0.5 and 1.0 lbs / hr, respectively, before passing over the catalyst. The resulting contact time was 12 seconds. The low boiling point components HCl and HCl-32 separated in the distillation column were passed through a caustic scrubber containing 10% KOH where HCl was removed. Purified HFC-32 was collected by drying. The conversion of the resulting HCC-30 was 90%, the selectivity for HFC-32 was 90% and the selectivity for HCFC-31 was 9%.

As described above, HFC-32 can be produced that exhibits good production yield and selectivity.

Claims (10)

(A) preheating the composition comprising hydrogen fluoride and dichloromethane to form an evaporated and superheated composition; (B) reacting the preheated composition of step (A) in the presence of a fluorination catalyst under conditions suitable to form a product stream comprising difluoromethane, chlorofluoromethane, hydrogen chloride, dichloromethane and hydrogen fluoride; (C) distilling from the product stream of step (B) a high boiling fraction comprising hydrogen fluoride, dichloromethane, and chlorofluoromethane and a low boiling fraction comprising difluoromethane, hydrogen chloride, hydrogen fluoride, and reaction byproducts Recovering by; And (D) recovering substantially pure difluoromethane from the low boiling fraction of step (C); Difluoromethane production method comprising a. The method of claim 1 wherein the hydrogen fluoride and dichloromethane are present in a molar ratio of about 1: 1 to about 10: 1. The method of claim 1 wherein the composition of step (A) further comprises chlorofluoromethane. The method of claim 1 or 3, wherein the hydrogen fluoride and chlorofluoromethane are present in the product stream in a molar ratio of at least about 25: 1 to at least about 300: 1. The process of claim 1 or 3, wherein the hydrogen fluoride and chlorofluoromethane are present in the product stream in a molar ratio of at least about 50: 1 to about 200: 1. The process of claim 1, wherein the hydrogen fluoride and chlorofluoromethane are present in the product stream in a molar ratio of at least about 75: 1 to at least about 150: 1. The method of claim 1 wherein the fluorination catalyst is a pretreated fluorination catalyst. 8. The method of claim 1 or 7, wherein the fluorination catalyst is chromium oxide. The method of claim 1 wherein the high boiling point fraction of step (C) is recycled to step (A). The method of claim 1, wherein step D further (E) treating the low boiling point mixture of step (C) in an HCl distillation column or an aqueous HCl adsorption column under conditions suitable to remove HCl and traces of HF to form a crude HFC-32 product; (F) treating the crude HFC-32 product formed in step (E) with a first caustic scrubber under conditions suitable to form a neutralized product; (G) treating said neutralized product of step (F) in a second caustic scrubber under conditions suitable to form a product which is actually chlorine free; (H) treating the substantially chlorine free product of step (G) with a sulfuric acid scrubber followed by a solid desiccant to form a product that is virtually moisture free; And (I) distilling said substantially moisture free product of step (H) under conditions suitable for producing substantially pure difluoromethane. Method comprising a lower step consisting of.